Low-temperature-resistant electrolyte for liquid capacitor and preparation method thereof

Abstract

The application discloses a low-temperature-resistant working electrolyte for liquid capacitors and a preparation method thereof, and relates to the technical field of electrolytes for capacitors. The low-temperature-resistant working electrolyte comprises the following raw materials: ethylene glycol, an auxiliary solvent, a solute, ammonium hypophosphite, a synergist, a stabilizer, 1-ethyl-3-methyl imidazolium bis(trifluoromethylsulfonyl) imide, boron nitride nanosheets and 2,2,2-trifluoroethyl acrylate. The application introduces the synergist which can improve the conductivity, the cycle life, the ion mobility at low temperature and the power density at low temperature, and the 2,2,2-trifluoroethyl acrylate which can further improve the electrochemical performance stability at low temperature, in addition to the auxiliary solvent with a specific proportion. In combination with the specific preparation method which can prevent agglomeration and improve the smoothness of the ion conduction path, the chemical performance of the electrolyte is more excellent at low temperature, and the application prospect is also wider.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electrolyte for capacitor, and particularly relates to a low-temperature-resistant electrolyte for liquid capacitor and a preparation method thereof. BACKGROUND

[0002] A liquid capacitor is generally composed of electrodes, electrolyte and isolation medium. Its working principle is based on the basic characteristics of the capacitor. When a voltage is applied to the two electrodes, the electrodes will respectively accumulate positive and negative charges. The ions in the electrolyte can move under the action of the electric field to assist the storage and release of the charges, thereby realizing the storage function of the electric energy. Common liquid capacitors are aluminum electrolytic capacitors and tantalum electrolytic capacitors. Among them, the aluminum electrolytic capacitor uses aluminum foil as the electrode and paper or other porous materials soaked with electrolyte as the isolation medium. Due to its lower cost, higher rated voltage, wider capacity range, mature production process, and wide material sources, the aluminum electrolytic capacitor has a more extensive application prospect in the fields of audio circuits, communication equipment, industrial control, automotive electronics, consumer electronics, etc.

[0003] The electrolyte of the aluminum electrolytic capacitor is composed of various chemical reagents according to the required conductivity and flash voltage, and is the real negative electrode of the capacitor. The main solvent is generally ethylene glycol and deionized water. Its conductivity directly affects the loss and equivalent series resistance value of the capacitor; the flash voltage determines the maximum voltage that the electrolyte can withstand; and the pH value affects the corrosion of the guide needle. Therefore, the electrolyte has a crucial influence on the electrochemical performance of the aluminum electrolytic capacitor. However, the existing electrolyte still has the problem of performance degradation at low temperature, which leads to poor electrochemical performance of the capacitor.

[0004] In order to solve this technical problem, patent technology document CN112768248B proposes a low-temperature-resistant electrolyte for aluminum electrolytic capacitor, which comprises the following components: ethylene glycol, propylene glycol, diethylene glycol, diethylene glycol monomethyl ether, dibutyl carbonate, butyl 2-methylbutyrate, solute, flash enhancer, hydration inhibitor, stabilizer, and hydrogen removal agent. The low-temperature-resistant electrolyte for aluminum electrolytic capacitor described in the invention has low capacity loss at low temperature and high flash voltage. By using ethylene glycol, propylene glycol, and diethylene glycol as the main solvent, and diethylene glycol monomethyl ether, dibutyl carbonate, and butyl 2-methylbutyrate as the auxiliary solvent, the solvent system of the invention is formed, which is beneficial to the movement of the ionization balance of the dielectric to the ionization direction, improves the formation ability of the electrolyte, enhances the solvation effect of the electrolyte solvent, and improves the activity of the electrolyte, thereby improving the low-temperature resistance and reducing the capacity loss at low temperature. However, these prior optimization methods are mostly optimized for the solvent system of the electrolyte, and the influence of other components on the performance of the electrolyte is not considered, so the improvement of the electrochemical performance of the electrolyte at low temperature is limited. SUMMARY

[0005] The application aims to provide a low-temperature-resistant electrolyte for liquid capacitors and a preparation method thereof, and solve the following technical problems:

[0006] The existing low-temperature-resistant electrolyte still has poor electrochemical performance and stability at low temperatures.

[0007] The application can be achieved by the following technical solutions:

[0008] The low-temperature-resistant electrolyte for liquid capacitors comprises the following raw materials by mass fraction: ethylene glycol 60-75 parts, auxiliary solvent 20-24 parts, solute 5-6.5 parts, ammonium hypophosphite 1.2-1.5 parts, synergist 2-5 parts, stabilizer 1-1.5 parts, adjusting agent 0.8-1.5 parts, 1-ethyl-3-methyl imidazolium bis(trifluoromethylsulfonyl) imide 3-6 parts, boron nitride nanosheet 0.1-0.2 parts, and 2,2,2-trifluoroethyl acrylate 2-3 parts.

[0009] Preferably, the synergist is prepared from manganese dioxide powder and niobium nitrate solution.

[0010] The stabilizer is any one of sorbitol and diammonium hydrogen phosphate.

[0011] The adjusting agent is any one of p-nitrophenol, p-nitrobenzyl alcohol, and p-nitrobenzoic acid.

[0012] Preferably, the auxiliary solvent is obtained by mixing diethylene glycol and propylene glycol.

[0013] The mass ratio of diethylene glycol to propylene glycol is 5-6.5:15-17.5.

[0014] Preferably, the solute is any one or more of tetraethylammonium tetrafluoroborate, ammonium hydrogen azelate, and formic acid.

[0015] Preferably, the preparation method of the synergist is as follows:

[0016] Step A1: Under an argon atmosphere, the manganese dioxide powder is subjected to low-temperature plasma treatment to obtain pretreated manganese dioxide.

[0017] Step A2: The pretreated manganese dioxide is added to the niobium nitrate solution, heated to 80-100 DEG C under stirring, then stirred for 7-10 h, and then filtered, washed, and dried to obtain the synergist.

[0018] Preferably, the pressure during the low-temperature plasma treatment in step A1 is 30-80 Pa; the power during the low-temperature plasma treatment is 80-160 W; the processing temperature during the low-temperature plasma treatment is 30-50 DEG C; and the processing time during the low-temperature plasma treatment is 10-25 min.

[0019] Preferably, the concentration of the niobium nitrate solution in step A2 is 0.01-0.1 mol / L.

[0020] Preferably, the ratio of the use amount of the pretreated manganese dioxide to the niobium nitrate solution in step A2 is 8.7-43.5 g:100 mL.

[0021] The application discloses a preparation method of a low-temperature-resistant working electrolyte for a liquid capacitor.

[0022] Step B1: an auxiliary solvent is added into ethylene glycol, and then a solute is added after uniform stirring, and the stirring is continued for 3-5 h to obtain a composite solvent;

[0023] Step B2: the ammonium hypophosphite, the synergist, the stabilizer, the regulator, 1-ethyl-3-methyl imidazolium bis(trifluoromethylsulfonyl) imide, boron nitride nanosheets and 2,2,2-trifluoroethyl acrylate are sequentially added into the composite solvent under stirring, and then the stirring is continued for 12-15 h under ultrasonic assistance to obtain the low-temperature-resistant working electrolyte.

[0024] Preferably, the ultrasonic power during the ultrasonic assistance in step B2 is 80-90 W; and the ultrasonic frequency during the ultrasonic assistance is 30-45 kHz.

[0025] As a further scheme of the application.

[0026] The application has the following beneficial effects:

[0027] The application provides a low-temperature-resistant working electrolyte for a liquid capacitor and a preparation method thereof.

[0028] (1) The present application effectively removes the organic contaminants, oxide layer or other impurities on the surface of the manganese dioxide powder by low-temperature plasma treatment, and at the same time, forms a micro-nano rough structure on the surface of the manganese dioxide, introduces oxygen-containing functional groups on the surface of the manganese dioxide, and improves the hydrophilicity of the surface of the manganese dioxide, thereby improving the interfacial bonding force between the manganese dioxide and the subsequent loaded niobium compound, so that the niobium ions in the niobium nitrate solution can be combined more closely and uniformly on the surface of the manganese dioxide, and the prepared synergist has more excellent ability to improve the conductivity, enhance the low-temperature stability, widen the electrochemical window, increase the specific capacity, improve the cycle stability, inhibit the side reaction, optimize the interface performance and improve the power density.

[0029] (2) The added 1-ethyl-3-methyl imidazolium bis(trifluoromethyl sulfonyl) imide has extremely low freezing point and high conductivity, which can significantly improve the low-temperature performance of the electrolyte, and the unique anion-cation structure can effectively inhibit the crystallization of the electrolyte at low temperature and improve the stability of the electrolyte.

[0030] (3) The addition of 2,2,2-trifluoroethyl acrylate can introduce a strong electron-withdrawing group trifluoromethyl, thereby reducing the viscosity of the electrolyte and improving the ion migration rate; at the same time, the polymer network formed after polymerization can stabilize the electrolyte structure and inhibit the decomposition of the electrolyte at low temperature.

[0031] (4) The ultrasonic assisted treatment during the preparation of the low-temperature resistant working electrolyte can effectively disperse boron nitride nanosheets and other nanomaterials, prevent agglomeration, reduce phase separation or precipitation in the electrolyte, make the ion conduction path in the electrolyte more unobstructed, reduce the interfacial impedance, and at the same time, accelerate the dissolution, dispersion and mixing process, and reduce the time required for traditional stirring.

[0032] Therefore, the low-temperature resistant working electrolyte prepared by the present application has more excellent low-temperature stability, conductivity, and more ideal flashover voltage value and other electrochemical properties. DETAILED DESCRIPTION

[0033] The technical solutions in the embodiments of the present application will be described below in a clear and complete manner. Obviously, the described embodiments are only a part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0034] Example 1: The preparation method of the low-temperature resistant working electrolyte for liquid capacitor is as follows:

[0035] S1: under an argon atmosphere, the manganese dioxide powder was subjected to low-temperature plasma treatment at a pressure of 30 Pa, a power of 80 W, a temperature of 30 DEG C, and a time length of 10 min to obtain pretreated manganese dioxide;

[0036] S2: 8.7 g of the pretreated manganese dioxide was added to 100 mL of a niobium nitrate solution with a concentration of 0.01 mol / L, heated to 80 DEG C under stirring, then stirred for 7 h, and after filtration, washing, and drying, a synergist was obtained;

[0037] S3: 5 g of diethylene glycol was uniformly mixed with 15 g of propylene glycol to obtain an auxiliary solvent;

[0038] S4: 20 g of the auxiliary solvent was added to 60 g of ethylene glycol, uniformly stirred, then 5 g of tetraethylammonium tetrafluoroborate was added, and the stirring was continued for 3 h to obtain a composite solvent;

[0039] S5: 1.2 g of ammonium hypophosphite, 2 g of the synergist, 1 g of sorbitol, 0.8 g of p-nitrophenol, 3 g of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide, 0.1 g of boron nitride nanosheet, and 2 g of 2,2,2-trifluoroethyl acrylate were sequentially added to 85 g of the composite solvent under stirring, and then the stirring was continued for 12 h under ultrasonic assistance at a power of 80 W and a frequency of 30 kHz to obtain a low-temperature-resistant working electrolyte.

[0040] Example 2: A low-temperature-resistant working electrolyte for a liquid capacitor was prepared according to the following method:

[0041] S1: under an argon atmosphere, the manganese dioxide powder was subjected to low-temperature plasma treatment at a pressure of 50 Pa, a power of 100 W, a temperature of 35 DEG C, and a time length of 15 min to obtain pretreated manganese dioxide;

[0042] S2: 15 g of the pretreated manganese dioxide was added to 100 mL of a niobium nitrate solution with a concentration of 0.03 mol / L, heated to 90 DEG C under stirring, then stirred for 8 h, and after filtration, washing, and drying, a synergist was obtained;

[0043] S3: 5.5 g of diethylene glycol was uniformly mixed with 15.5 g of propylene glycol to obtain an auxiliary solvent;

[0044] S4: 21 g of the auxiliary solvent was added to 65 g of ethylene glycol, uniformly stirred, then 5.5 g of ammonium hydrogen azelate was added, and the stirring was continued for 3.5 h to obtain a composite solvent;

[0045] S5: while stirring, 1.3 g of ammonium hypophosphite, 3 g of the synergist, 1.2 g of diammonium hydrogen phosphate, 1.0 g of p-nitrobenzyl alcohol, 4 g of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide, 0.13 g of boron nitride nanosheets, and 2.3 g of 2,2,2-trifluoroethyl acrylate were sequentially added to 91.5 g of the composite solvent, and then stirring was continued for 13 h under ultrasonic assistance at a power of 83 W and a frequency of 35 kHz to obtain the low-temperature-resistant working electrolyte.

[0046] Example 3: The low-temperature-resistant working electrolyte for a liquid capacitor was prepared as follows:

[0047] S1: The manganese dioxide powder was subjected to low-temperature plasma treatment under an argon atmosphere at a pressure of 45 Pa, a power of 110 W, a temperature of 40°C, and for a time period of 20 min to obtain pretreated manganese dioxide;

[0048] S2: 30 g of the pretreated manganese dioxide was added to 100 mL of a niobium nitrate solution with a concentration of 0.07 mol / L, heated to 90°C under stirring, and then stirred for 9 h, followed by filtration, washing, and drying to obtain the synergist;

[0049] S3: 6 g of diethylene glycol was uniformly mixed with 17 g of propylene glycol to obtain an auxiliary solvent;

[0050] S4: 23 g of the auxiliary solvent was added to 70 g of ethylene glycol, stirred uniformly, and then 3 g of formic acid and 3 g of tetraethylammonium tetrafluoroborate were added, and stirring was continued for 4 h to obtain the composite solvent;

[0051] S5: while stirring, 1.3 g of ammonium hypophosphite, 3 g of the synergist, 1.2 g of diammonium hydrogen phosphate, 1.0 g of p-nitrobenzyl alcohol, 4 g of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide, 0.13 g of boron nitride nanosheets, and 2.3 g of 2,2,2-trifluoroethyl acrylate were sequentially added to 91.5 g of the composite solvent, and then stirring was continued for 13 h under ultrasonic assistance at a power of 83 W and a frequency of 35 kHz to obtain the low-temperature-resistant working electrolyte.

[0052] Example 4: The low-temperature-resistant working electrolyte for a liquid capacitor was prepared as follows:

[0053] S1: The manganese dioxide powder was subjected to low-temperature plasma treatment under an argon atmosphere at a pressure of 80 Pa, a power of 160 W, a temperature of 50°C, and for a time period of 25 min to obtain pretreated manganese dioxide;

[0054] S2: 43.5 g of the pretreated manganese dioxide was added to 100 mL of a niobium nitrate solution with a concentration of 0.1 mol / L, heated to 100°C under stirring, and then stirred for 10 h, followed by filtration, washing, and drying to obtain the synergist;

[0055] S3: Mix 6.5g of diethylene glycol and 17.5g of propylene glycol evenly to obtain an auxiliary solvent;

[0056] S4: Add 24g of auxiliary solvent to 75g of ethylene glycol, stir evenly, then add 4g of tetraethylammonium tetrafluoroborate, 2g of formic acid, and 0.5g of ammonium hydrogen azelate, and continue stirring for 5h to obtain a composite solvent;

[0057] S5: While stirring, add 1.5g ammonium hypophosphite, 5g synergist, 1.5g diammonium hydrogen phosphate, 1.5g p-nitrobenzoic acid, 6g 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, 0.2g boron nitride nanosheets, and 3g 2,2,2-trifluoroethyl acrylate to 105.5g composite solvent in sequence. Then, continue stirring for 15h under ultrasonic assistance at a power of 90W and a frequency of 45kHz to obtain a low-temperature resistant working electrolyte.

[0058] Comparative Example 1:

[0059] Compared with Example 1, this comparative example only replaces the "pretreated manganese dioxide" added during the preparation of the synergist with "manganese dioxide powder". All other steps and parameters are the same, and will not be repeated in this comparative example. Finally, a low-temperature resistant working electrolyte is obtained.

[0060] Comparative Example 2:

[0061] Compared with Example 1, this comparative example only replaces "5g diethylene glycol and 15g propylene glycol" added during the preparation of the auxiliary solvent with "15g diethylene glycol and 5g propylene glycol". All other steps and parameters are the same, and will not be repeated in this comparative example. Finally, a low-temperature resistant working electrolyte is obtained.

[0062] Comparative Example 3:

[0063] Compared with Example 1, this comparative example only replaces "1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide" added during the preparation of the low-temperature working electrolyte with "2,2,2-trifluoroethyl acrylate". All other steps and parameters are the same, and will not be repeated in this comparative example. The final low-temperature working electrolyte is obtained.

[0064] Comparative Example 4:

[0065] Compared with Example 1, this comparative example only replaces "2,2,2-trifluoroethyl acrylate" added during the preparation of the low-temperature working electrolyte with "1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide". All other steps and parameters are the same, and will not be repeated in this comparative example. The final low-temperature working electrolyte is obtained.

[0066] Comparative Example 5:

[0067] This comparative example differs from Example 1 only in that it did not use ultrasonic assistance in the preparation of the low-temperature working electrolyte. All other steps and parameters are the same, and will not be repeated here. The final low-temperature working electrolyte was obtained.

[0068] Performance testing:

[0069] Measurement of conductivity:

[0070] 15 mL of electrolyte was loaded into a CT-57101B type measuring battery manufactured by DKK East Asia. The temperature of the constant temperature bath was adjusted to 30°C. After the electrolyte temperature reached 30°C, its conductivity was measured. The conductivity (mS·cm) of the low-temperature resistant working electrolytes prepared in Examples 1-4 and Comparative Examples 1-5 was measured according to this method. -1 The measurement results are shown in Table 1.

[0071] pH value measurement:

[0072] The electrolyte temperature was adjusted to 25°C, and the pH value of the electrolyte was measured using a DST-5421C pH meter manufactured by DKK East Asia. The pH values ​​of the low-temperature resistant working electrolytes prepared in Examples 1-4 and Comparative Examples 1-5 were measured according to this method, and the results are shown in Table 1.

[0073] Determination of flash point voltage:

[0074] High-voltage chemically etched aluminum foil was used as both anode and cathode, and a GP650-05R manufactured by Takasago Semiconductor was used as a DC stabilized power supply. The readings showed constant current under load at -60°C (current density: 10 mA / cm²). 2 The voltage value observed when the voltage drops (short circuit) is used as the flashover voltage. The flashover voltage (V) of the low-temperature resistant working electrolytes prepared in Examples 1-4 and Comparative Examples 1-5 were measured according to this method, and the results are shown in Table 1.

[0075] Stability determination:

[0076] The electrolyte was placed in a transparent glass bottle and placed in a constant temperature bath at -60°C for 24 hours. The bottle was then tilted at -60°C and visually observed. Evaluation was based on the following criteria: Pass: Transparent, no precipitates, and fluid when tilted; Good: Slightly turbid, but no precipitates, and fluid when tilted; Fail: Completely solidified. The stability of the low-temperature working electrolytes prepared in Examples 1-4 and Comparative Examples 1-5 was determined using this method, and the results are shown in Table 1.

[0077] Measurement of capacitance loss:

[0078] The capacitance values ​​of the electrolyte were measured and recorded at 20°C and -60°C using the same method. The capacitance loss at -60°C (relative to 20°C) was then calculated. The capacitance loss (%) of the low-temperature working electrolytes prepared in Examples 1-4 and Comparative Examples 1-5 was measured using this method, and the results are shown in Table 1.

[0079] Table 1: Performance test results of Examples 1-4 and Comparative Examples 1-5

[0080]

[0081] Data Analysis:

[0082] As can be seen from Table 1, the low-temperature resistant working electrolyte prepared by the present invention has better low-temperature stability, conductivity, and more ideal electrochemical properties such as flashover voltage and capacitance loss.

[0083] This is likely because the present invention, through low-temperature plasma treatment of manganese dioxide powder, effectively removes organic contaminants, oxide layers, or other impurities from the surface of the manganese dioxide powder. Simultaneously, it forms a micro-nano-scale rough structure on the manganese dioxide surface, introduces oxygen-containing functional groups, and improves the hydrophilicity of the manganese dioxide surface. This, in turn, improves the interfacial bonding force between manganese dioxide and the subsequently loaded niobium compound, allowing niobium ions in the niobium nitrate solution to bind more tightly and uniformly on the manganese dioxide surface. Furthermore, the prepared synergist exhibits superior capabilities in improving conductivity, enhancing low-temperature stability, broadening the electrochemical window, increasing specific capacity, improving cycle stability, suppressing side reactions, optimizing interfacial properties, and increasing power density. The specific proportion of auxiliary solvent added in this invention can lower the freezing point of the solvent system, improve low-temperature viscosity, increase conductivity, enhance thermal stability, optimize solvation effects, suppress crystallization and phase separation, improve wettability, and generate synergistic effects, thereby maximizing the electrochemical performance of the electrolyte at low temperatures. The 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide added in this invention has an extremely low freezing point and high conductivity, which can significantly improve the low-temperature performance of the electrolyte. Simultaneously, its unique anionic and cationic structure can effectively inhibit the crystallization of the electrolyte at low temperatures, improving its stability. The addition of 2,2,2-trifluoroethyl acrylate introduces the strong electron-withdrawing trifluoromethyl group, thereby reducing the viscosity of the electrolyte and increasing ion mobility. Furthermore, the polymer network formed after polymerization can stabilize the electrolyte structure and inhibit decomposition at low temperatures. The ultrasonic-assisted treatment during the preparation of the low-temperature working electrolyte in this invention can effectively disperse boron nitride nanosheets and other nanomaterials, preventing their aggregation. It can also reduce phase separation or precipitation in the electrolyte, promote uniform dispersion and thorough mixing of components, making the ion conduction pathway in the electrolyte smoother and reducing interfacial impedance. At the same time, it accelerates the dissolution, dispersion, and mixing processes, reducing the time required for traditional stirring. Therefore, the low-temperature resistant working electrolyte prepared by this invention has superior low-temperature stability, conductivity, and more ideal flashover voltage and other electrochemical properties.

[0084] The foregoing has provided a detailed description of one embodiment of the present invention, but this description is merely a preferred embodiment and should not be construed as limiting the scope of the invention. All equivalent variations and modifications made within the scope of the claims of this invention should still fall within the patent coverage of this invention.

Claims

1. A low-temperature resistant working electrolyte for liquid capacitors, characterized in that, The raw materials include the following parts by weight: 60-75 parts ethylene glycol, 20-24 parts auxiliary solvent, 5-6.5 parts solute, 1.2-1.5 parts ammonium hypophosphite, 2-5 parts synergist, 1-1.5 parts stabilizer, 0.8-1.5 parts regulator, 3-6 parts 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, 0.1-0.2 parts boron nitride nanosheets, and 2-3 parts 2,2,2-trifluoroethyl acrylate; The synergist is prepared from manganese dioxide powder and niobium nitrate solution; The stabilizer is either sorbitol or diammonium hydrogen phosphate; The regulator is any one of p-nitrophenol, p-nitrobenzyl alcohol, and p-nitrobenzoic acid; The preparation method of the synergist is as follows: Step A1: Under an argon atmosphere, manganese dioxide powder is subjected to low-temperature plasma treatment to obtain pretreated manganese dioxide; Step A2: Add pretreated manganese dioxide to niobium nitrate solution, heat to 80-100℃ under stirring, stir for 7-10 hours, and then obtain the synergist after filtration, washing and drying.

2. The low-temperature resistant working electrolyte for liquid capacitors according to claim 1, characterized in that, The auxiliary solvent is obtained by mixing diethylene glycol and propylene glycol; The mass ratio of diethylene glycol to propylene glycol is 5-6.5:15-17.

5.

3. The low-temperature resistant working electrolyte for liquid capacitors according to claim 1, characterized in that, The solute is any one or more of tetraethylammonium tetrafluoroborate, ammonium azelaate, and formic acid.

4. The low-temperature resistant working electrolyte for liquid capacitors according to claim 1, characterized in that, The pressure during the low-temperature plasma treatment in step A1 is 30-80 Pa; the power during the low-temperature plasma treatment is 80-160 W; the treatment temperature during the low-temperature plasma treatment is 30-50 °C; and the treatment time during the low-temperature plasma treatment is 10-25 min.

5. The low-temperature resistant working electrolyte for liquid capacitors according to claim 1, characterized in that, The concentration of the niobium nitrate solution mentioned in step A2 is 0.01-0.1 mol / L.

6. The low-temperature resistant working electrolyte for liquid capacitors according to claim 1, characterized in that, The ratio of manganese dioxide to niobium nitrate solution used in step A2 is 8.7-43.5 g: 100 mL.

7. The method for preparing the low-temperature resistant working electrolyte for liquid capacitors according to claim 1, characterized in that, The preparation method is as follows: Step B1: Add an auxiliary solvent to ethylene glycol, stir until homogeneous, then add the solute and continue stirring for 3-5 hours to obtain a composite solvent; Step B2: While stirring, add ammonium hypophosphite, synergist, stabilizer, regulator, 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, boron nitride nanosheets, and 2,2,2-trifluoroethyl acrylate to the composite solvent in sequence. Then, continue stirring for 12-15 hours under ultrasonic assistance to obtain a low-temperature resistant working electrolyte.

8. The method for preparing the low-temperature resistant working electrolyte for liquid capacitors according to claim 7, characterized in that, The ultrasonic power during ultrasound assistance in step B2 is 80-90W; the ultrasonic frequency during ultrasound assistance is 30-45kHz.

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